Energy changes Flashcards
What is an exothermic reaction
When energy is given out to the surroundings
What is an endothermic reaction
When energy is taken in from the surroundings
If rectants have more energy than products, what type of reaction is it
Endothermic
What is breaking bonds
Exo or endo
Endothermic
What are two examples of an exothermic reaction
Burning fuels- Combustion
Neutralisation (Acid + Alkali–> Salt + Water)
What is an example of an endothermic reaction
Thermal decomposition
What is a real life use of exothermic reactions
Instant hand warmers
What is a real life use of endothermic reactions
Instant sports ice packs
If there is an exothermic reaction on a graph, will the line be above or below the initial point
Below
What is the peak amount of energy reached during a reaction called
Activation energy
What do you need to break bonds
Energy/ heat
What is released when new bonds form
Energy
What is an electrochemical cell
A system where there are two different electrodes in contact with an electrolyte.
What are the electrodes typically made out of
Metals
What is an electrolyte
A liquid that is able to carry charge. It contains ions that react with the electrodes
How does a simple battery work
The chemical reactions between the electrodes (which are connected at the top) and the electrolyte set up a charge difference between the electrodes.
This means electricity will flow from the more reactive metal to the less reactive metal.
What does the voltage of a cell depend on
- The metals used
- The type of electrolyte
What is a battery and how do you make one
A battery is two or more cells connected in series
You can make a battery by connecting different cells
Why do sime batteries run out of charge
Because all of the reactants are used up and the reaction is irreversible
What type of batteries are non rechargeable and why
Alkene batteries are non renewable
This is because te reaction is irreversible
How are rechargeable batteries recharged
The reaction is reversed by connecting an external electric current
What is a fuel cell
An electrical cell that is supplied with fuel and oxygen
Uses energy from the reaction to produce electrical energy
What happens to fuel when it enters the fuel cell
The fuel is oxidised. This sets up a potential difference within the cell
What are the reactants and products in a hydrogen fuel cell
Reactants:
Hydrogen and oxygen
Products:
Water and energy
How is a hydrogen fuel cell set up
Electrolyte (potassium hyroxide) in the middle
Carbon Anode (negative) on the left
Carbon Cathode (positive) on the right
REVERSE OF ELECTROLYSIS
Both electrodes have inlets on the sides
Hydrogen goes into anode
Oxygen goes into cathode
All water and heat leaves through outlet of cathode
How does a hydrogen fuel cell work
Hydrogen comes in and is oxidised by anode
Hydrogen becomes an ion
Electrons pass around the wire to the cathode, while the hydrogen moves through the electrolyte to the cathode
Electrons and hydrogen ions react with oxygen to produce water
Water leaves by outlet
What is the half equation of oxidation of hydrogen in fuel cells
H₂ —> 2H(+) + 2e(-)
What is the half equation of the reaction of hydrogen ions and water at the positive electrode
O₂ + 4H(+) + 4e(-) –> 2 H₂O
What is the overall equation in a fuel cell
2H₂ + O₂ —> 2H₂O
What are some advantages of hydrogen fuel cells
- Less polutants/ emissions
- More reusable than electric batteries
- Cheaper than electricc batteries
- Can store more energy than typical batteries
What are some disadvantages of hydrogen fuel cells
- Hydrogen is a gas so it takes up more space
- Hydrogen is explosive so must be handled with care
- Hydrogen is made from electrolysis which uses energy that could be releasing emissions